In the processing of substrates, such as semiconducting wafers, a substrate is placed on a support in a processing chamber while suitable processing conditions are maintained in the processing chamber. A rapid thermal processing (RTP) chamber may be used to heat the substrate with lamps disposed below the substrate. For example, a substrate could be rapidly heated to an elevated temperature within a temperature range of 250° C. to 1,350° C. During a thermal process, a substrate may be supported by a supporting structure, such as an edge ring, around the edge region of the substrate. The edge ring may be supported by another supporting structure, such as a support ring.
The edge ring and support ring are constructed of materials that can withstand numerous cycles of being rapidly heated and cooled. Quartz (e.g., amorphous silica) is a material often used for the support ring structure. When heating a substrate from below with lamps in a RTP chamber, it is typically desirable to block lamp radiation from entering the area above the substrate in the RTP chamber. Radiation sensors that are sensitive to radiation emitted by the substrate, such as pyrometers, are often used in the area above the substrate. Preventing lamp radiation from entering the area above the substrate prevents radiation from hampering performance of the temperature sensors. Because quartz is transparent to light and infrared energy, the upper surface of a quartz support ring is often coated with a material, such as silicon, to render it opaque to the lamp radiation.
Quartz support rings coated with silicon begin to develop cracks in the radial direction after being repeatedly heated and cooled. The cracks may begin to develop after only a few heating cycles. The cracks eventually make the quartz support rings coated with silicon unusable, and frequent replacement of support rings is not cost effective.
Therefore, a need exists for improved quartz support rings having opaque coatings.